Fuse



Oct. 8, M' J. SAND|N FUSE Filed Aug. 6, 1923 Patented Oct. 8, 1929 UNITED STATES PATENT .oFFtcE l MAUBITS J'. SANDIN, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYL- VANIA FUSE Application mea August s, 1923. serial No. 655,811.

My invention relates to fuses and particularly to fusible strips used in fuses of the expulsion cartridge type or of the closed cartridge type for interrupting electric circuits under overload and short-circuit conditions.

One ob'ect of my invention is to provide a renewa le fuse strip suitable for use in fuse cartridges closed at both ends or in fuse cartridges of the expulsion fuse type wherein one of the ends of the cartridge is open for pemitting the escape of gases from the end thereof when the circuit is interrupted.

Another object of my invention is to provide a fuse strip having the above characteristics that may be used in high potential circuits for interrupting the circuit upon the passage of a comparatively low amount of current, such, for instance, as one ampere or a fractional part thereof.

Another object of my invention is to pro-v vide a fuse strip particularly applicable for use in expulsion fuses wherein a fuse strip of comparatively small cross-sectional area may be used for interrupting small currents in high potential circuits and wherein the fuse strip is reenforced by a stri of insulation to prevent breakage of the filsible strip during shipment and the assembly operation.

These and other objects that will be made apparent throughout the further description V of my invention are attained by means of the fusible device herein described and illustrated in the accompanying drawings, wherein Figure 1 is a longitudinal sectional view through an expulsion fuse cartridge containing the improved fuse strip,

Fig. 2 is an elevational view of the fuse strip shown in Eig. 1, and

Fig. 3 is a transverse sectlonal view taken on the line III- III of Fig. 2.

Referring to the drawings, the improved fuse strip is shown applied to an expulsion fuse cartridge similar to that illustrated and described in my co-pendin g application Serial No. 510,280, filed October 25, 1921. The fuse cartridge comprises an insulating tube 4 that is threaded at one end for receiving a threaded terminal bushing 5 that is adapted to engage terminals on a fuse cartridge support (not shown). The bushinfr 5 is provided with a threaded cap 6 for c osing the end of the tube. A fuse terminal 7 is attached to the interior of the bushing 5. The lower end of the insulating tube is provided with a metal bushing' 8 for engaging terminals on the support referred to above. A fuse terminal 9 is attached to the bushing 8 and is provided with a fuse clamp 11 that is retained in clamping position by means. of a screw 12. rlhe fuse terminal 7 is also provided with a fuse clamp 13 that is retained in position by a clamping screw 14.

An insulating tube 15 is loosely mounted i within the tube 4 and is retained in o erative position by means of a fuse strip 16 t iat will be herein after described in detail. The eX- pulsion tube just described forms no part of my invention and is shown for the purpose of illustrating the application of the improved fuse strip.

The fuse strip comprises a relatively heavy strip, 17 of zinc or other fusible metal, at one end of which is attached, by means of rivets 18, a relatively thin strip of tin foil 19 having a relatively low current-carrying capacity and adapted to be ruptured by relatively small currents, such as an ampere or less. The capacity of the tin foil strip may be varied by .cutting notches 21 in the strip and thereby leaving a portion 22 of reduced cross-sectional area or by varying the thickness of the tin foil strip. The tin foil strip is not of sulficient strength to withstand shocks incident to shipping and assembly, and in order to reenforce the strip, it is pasted, by means of a suitable cement or adhesive, or is otherwise att-ached, to an insulating strip 28 which is secured to the heavy zinc strip 17 by the rivets 18 in such manner that one end of the tin foil strip 19 is disposedfin conductive engagement with the strip 17 and between the latter and the insulating strip. By reason of the insulating re-enforcing strip, the fuse strip may be handled without danger of injuring the thin strip of tin foil.

lVhen the fuse strip is inserted in the expulsion fuse cartridge, the tin foil strip is placed in engagement with the terminal 7 and the end of the strip securely clamped thereto by the clamping plate 13 and screw" 14. The other end of the fuse strip is attached in the usual manner to the terminal 9 bymeans of the clamping plate 11 and the screw 12. A

When an overload or short-circuit condition prevails in the circuit in which the fuse is connected, the tin foil strip 19 Will be ruptured at the point of reduced cross-sectional area. The intense heatincident to the rupture of the fuse strip burns the insulating strip 23, which releases the upper end of the zinc strip 17. The gases within the closed end of the fuse cartridge then cause any unvolatilized portion of the zinc strip and the insulating tube 15 to be discharged from the open end of the cartridge, thereby extinguishing the arc. The construction is simple and inexpensive and it will readily be seen that the fuse strip may be used in other forms of fuse cartridges and that the strip is applicable for use in renewable fuses of either the closed or the vented cartridge type.

While I have illustrated but one embodiment of my invention, it'will be apparent t0 those skilled in the art that various changes, modifications, substitutions, additions and omissions may be made in the apparatus illustrated Without departing from the spirit and scope of my invention, as set forth in the appended claims.

I claim as' my invention:

1. A composite unitary structure constituting a fuse strip having a relatively heavy fusible metal strip, a separate strip of fusible metal of reduced cross-sectional area conductively connected thereto and a strip of insulaheavy fusible metal strip having a fusible metal extension of reduced current-carrying capacity and physical 'strength and a strip of insulation secured to the heavy fusible metal strip for reinforcing and supporting the said extension and adapted to be severed to release the heavy fusible metal strip upon the rupture of the extension of reduced carrying capacity.

6. The combination with a fuse casing hav-- ing a closure member for one of its ends, of a unitary fuse element therefor comprising two joined fusible members of substantially different strength, the weaker member being reinforced by insulation means and attached to the stronger member, the said unitary fuse element being supported in the fuse casing in a mannerthat the weaker reinforced member is adjacent'the closure member.

tion connected to the first fusible metal strip for reinforcing and supporting the second fusible metal strip.

2. A fuse strip comprising a relatively heavy fusible metal strip having an extension of a dierent fusible metal of reduced currentcarrying capacity and physical strength and a strip of insulation secured to the `first said fusible metal strip for reinforcing and supporting the said extension.

3. A fuse strip comprising a fusible metal strip Yconstituting a relatively heavy terminal engaging portion, a separate fusible metal strip of reduced current-carrying capacity for engaging another terminal and connected to the first strip and an insulating reinforcing strip connected to the rst fusible metal strip for reinforcing the fusible metal strip.

4. A fuse strip comprising a relatively strong fusible metal strip having a strip of insulation secured to the end thereof and constituting a terminal receiving extension, and a relatively Weak fusible strip of different metal conductively connected to the first said fusible metal strip and cemented to the'strip of insulation. 5. A fuse strip comprising a relatively 

